Integrated circuit (IC) manufacturers typically test their IC packages before shipping to customers using IC testing systems. A typical IC testing system 100, depicted in FIG. 1, includes a device handler 102, an interface structure 104, a device tester 106, and a computer 108. The device handler 102 is a precise robot that is utilized to move a device under test (DUT) 110, such as a packaged IC device, to, from, and within the testing system 100 (for example, between a storage area and the interface structure 104).
The interface structure 104 includes a printed circuit board (PCB) 112 having a socket 114 located in a central test area. The PCB 112 is of a size and shape that allows it to be received into a docking area of the device tester 106. The socket 114 includes a plurality of compressible pins such as pogo pins 116 arranged so as to contact corresponding balls 118 of the DUT 110 (e.g., the arrangement of pogo pins 116 of the socket 114 corresponds to the arrangement of balls 118 of the DUT 110).
The PCB 112 includes conductive contacts (not shown) disposed on a bottom surface thereof. The conductive contacts couple corresponding pogo pins 116 of the socket 114 to a plurality of test probes (not shown) of the device tester 106 by conductive lines 122 (e.g., metal traces). The plurality of test probes provide test signals to the interface structure 104, which in turn transmits signals between the device tester 106 and the leads (e.g., solder balls 118) of the DUT 110.
The computer 108 is coupled to the device tester 106. The computer 108 may be, for example, a personal computer (PC) or other suitable controller for controlling the testing system 100 and includes well-known testing software residing in memory (e.g., a system memory or a hard disk). The testing software provides test and control signals to device tester 106 according to test parameters associated with the DUT 110. The test parameters may be stored in a file located in computer memory, or may be input into the computer 108 using any suitable input device such as, for example, a keyboard (not shown).
In operation, the DUT 110 is mounted on the socket 114 (for example, using the device handler 102) so that the solder balls 118 contact the pogo pins 116 of the socket 114. The device handler 102 is configured to apply a pre-determined force against the DUT 110 based upon the height of the DUT 110. However, standard IC package sizes allow for a variety of heights for a given package size. For example, a 1 by 1 inch package can have a height that varies between about 0.25 to about 0.5 inches. Typically, device packages of a given size (e.g., x by y) utilize the same device handler and change kit for the testing system 100, even though there is a large variation in package heights (e.g., z direction). As such, damage to the packages being tested and/or the equipment may occur if the testing system is set up for processing smaller height packages and larger packages are actually being tested. Although some systems contain sensors for detecting stacked packages (e.g., two packages stacked atop each other), such sensors do not detect the height of the stacked packages.
Accordingly, there exists a need in the art for improved methods and apparatus for testing ICs.